The tree ferns are the ferns that grow with a trunk elevating the fronds above ground level. Most tree ferns are members of the "core tree ferns", belonging to the families Dicksoniaceae, Metaxyaceae, and Cibotiaceae in the order Cyatheales. In addition to those families, many ferns in other groups may be considered tree ferns, such as several ferns in the family Osmundaceae, which can achieve short trunks under a metre tall, and particularly ferns in the genus Cibotium, which can grow ten metres tall. Fern species with short trunks in the genera Blechnum, Calochleana, Cnemedaria, Culcita (Europe's only tree fern), Cystodium, Leptopteris, Lophosoria, Sadleria, Thyrsopteris and Todea could also be considered tree ferns in a liberal interpretation of the term.

The fronds of tree ferns are usually very large and multiple-pinnate. Tree ferns do not form new woody tissue in their trunk as they grow. Rather, the trunk is supported by a fibrous mass of roots that expands as the tree fern grows.

If the crown of Dicksonia antarctica (the most common species in gardens) is damaged, it will inevitably die because that is where all the new growth occurs. But other clump-forming tree fern species, such as D. squarrosa and D. youngiae, can regenerate from basal offsets or from "pups" emerging along the surviving trunk length. Tree ferns often fall over in the wild, yet manage to re-root from this new prostrate position and begin new vertical growth.

It is not certain the exact number of species of tree ferns there are, but it may be closer to 600-700 species.[1]